Hexamethylbenzene bf3 hf complex and solution thereof



HEXAMETHYLBENZENE BFs HF COMPLEX SOLUTION THEREOF David A. McCaulay,Chicago, I ll., Arthur P. Lien, H l nd, s n r t .sta da 'o l any,Chicago, 111., a corporation of Indiana Continuation of applicationSerial No. 14 6,7 76, February This application July 23, 1952, SerialNo.

2 Claims. (Cl. 252-3428) This invention relates to a novel complexcompound and more particularly, to'the complex compoundderived by thereaction of hexamethylb enze ne, BF: andI IF. One objectofjthe'p'rfe'sent'invention is to provide a novel complex compoundderived 'from hexamethylben'zene, 3P3 and HF. Another object ofthisginvention is to rovide a solution of a complex compound derivedfroin liexamet hylbenzenq'lBl a' and HF'in a solvent consistingessentially of liquid hydrogen fluoride." Another object ofthisinventionis to provide processes forthe preparatioh of a complex compound ofhexamethylbenzene, B Fs and HF. additional object ofthe invention'is'toprov e various uses for 'the complex compound of hexa- Complexcorrnqounds derived from various alkyl aromatte jhYd 'c ttb h' JBFs aHF' e Pre i us y ee prepared'loi'ftheir preparation has been ggested.For

BerhardQL/Evering proposestheabs orption ofiBFs in'a Imix'ture fof QI-IFand an 'alkylarorrlatic hydrocarbon conitiiiinirig 7 to 11 carbon atoms'pefmolecule" in order lto f rm ,an HF-soluble complex compound. U. SfPatent .397395 at ArthurP. Lienand'Bernard H. Shoem'a1l;ei-, "disclosescomplexes deriyed' fr'ozriB F, HF and" a aroiha'tic hydrocarbon 'su chas toluene, an ethyltolu'ene and diethylhenzienes'.ofo'rejbelievedrequisite that an" aromatic hydrocarboii w th at leastone"unsubstit lted 'rii1clear carbodatom to permit thef ormation of afcompl'ex compound by rea .W ave ad t ee P et 15enz ne," 1 ush" .7nuclear carbon atomfin the I benzene r g, r rapidly readily with .,B F3and LHF to p duc'e afcidrnpliex, having the more nnrformulahexan'iethyl- TbenZeneBFal-IF, which is readily soluble infree,great- Jhatthe relative basicity of hexamethylbenzene is of'the der of10 times the basicity of the next most basic ime y -subs iwie benzen a h'ip ds 9 4% times the basicity of I the. first methyl-substitutedbenzene h se basi city can be readily measured by its r eaetion .i i B53a HF tp-a z l h IwmP Xp mPQn ofr'hexamet hylbenzene, BB3 and HP ischaracterized by its relatively; low vapor pressure at moderatetemperatures,

which indicates that at these temperaturesit issubstantial-lyundissoeiate'd, since the freeHF and BF3 which are formedupondissociation have relatively high vapor pressu es: The novel'complex cornpound 'of'thi's invenft i dnypreierablyinthe formo'f itssolution infree liquid drog'en fluoride, is" adaptable to a ntnnben ofuses, yvhich 'cliscussed hereinafter. Further consideration yvillwithdrawn from the lower portioncf the toys/er as j'a 'mixture ofhexarnethylbenzene and mes'itylene ,(0;119 incl Iof Teach), 33.5 grams,in I 2111, in solution in 1-35 n- Tfheptane was placed in a magneticallystir'redcopper cat thtemperature of aDry' Ice-acetone bath." "ll-lydr o-2,727,011 Patented Dec. 13, 1955 ice . 2 be devoted at this point tomethods for the preparation of the hexam'ethylb'en zene complex.

Hexamethylbenzene reactsin the solid state or in solution'in otherhydrocarbons yvi'th 'BFs and HF by an exothermicreaction. [The rate ofthe reaction isvery rapid and it appears to be'ljrnited 'only by therate of mixing. In large scale preparations it'would be'defs'irable toremove at least a part of theheat of'reactio'n ih order to maintain 'thetemperature ofthe reaction mixture thin the desired limits to preventexcessiveyaporizaition of HF and thedevelopment of excessiy ely highpressures. Theordenoffnixing the"reagehts"does not app'e'af" to affectthe reaction? The'prese'n'ceof a'n excessofhydroge'n fiiiorid e', i. e,more'than 1" incl per mol of hexarn' thyl lb'en zene reactingj is'desirable," sirice"itfcanserv as persing medium for solid"hexamethylbenze'ne functions as a solvent for thdcoirhplex com'ponn: ofilfexai riet hylbenzend BE: and' 'fiFF ln general, Weinf y etnpl'oy'between about S'andabOut'ZO m I's of moi of hexamethylbenzen'e; althougheveh rnofe maybe "does not appear to be a criticaljvariableprovidedthatgit be su condition-in the reaction zone.

" thoughfas pointed out above, hexamethylbenzene infthe fsolid statereacts readily wanna-germinate sometimes necessary or'more convenient"toemploya "solution ofhexamethylbenzene "in "a diluent solvent,

for example, an'arornatic hydrOcarbQn suchaS benze :methyl-s ubstituted"benienesfsuch *as'fitoluiene, x enes, in'es itylene,tetramethylbenienesor the l ikle; or"in soluen's in" an aliphaticfhydrocarbon or mixturescontaining aliphatic hydrocarbons; for-example, 'pentanefpet leur'nether, n-heptane, petroleumnaphthas and'the "1i e."Th'e above-mentionedsolvents aremerely illustrative and it will be understood that any inertsolvent or" diluent can be empioyedfife. a solvent or diluent which doesnot react with thehexame'thylbermene, BFs or under the conditions towhich hexamethylbenzene is subjected to fi illfi 2iCOIHPIGXCOIIIPO'UUGIW' i The hexamethylbenz eheBFs.HF complex may beformed merely by agitating hexametliylbenzene' With an excess of'HF andBFs. at room'temperature and then pumping off the excess reagents? onemethod of prepar- 'ing a solution of this complex in HF is to passBFajinto a slurry of ,hexamethylb enzene in excessHF until'no furtherabsorption of BF; occurs. In another method of preparing the complexcompound of th is invention, a bed of solid hexamethylbenzfene ismaintained infa toyv e'r, "liquid HFTis trickled downwardlylthfou'ghth'efbed and a gas mixture comprising'BFs is passe'd upwardlythrougih "the bed, 'vvhereupon reactionenslies and the complexissolution in liquid hydrogen fluoride' .flhefollowing preparation isillustrative of the selective production of 'hexamethylbenzene.BFa'HFcomplex com- 'p'oundinthe presence of a diluent methyl -s'ubsiitnt'edbenzenef andjan aliphatic hydrocarbon diluent. An equiniblar genfluoride in the amount of 143 g. was then distilled into and condensedin the reactor, which was then cooled in a liquid nitrogen bath while8.5 g. of BFs were added. The reaction mixture was stirred and allowedto warm up to about 20 0, following which stirring was discontinued andthe contents of the reactor were allowed to settle for 15 minutes. Thelower, predominantly hydrofluoric acid phase was discharged from thereactor. An upper, predominantly hydrocarbon phase remained in thereactor. A clean-cut separation of the two phases was readily obtainedbecause of their marked differences in color and viscosity. In order todetermine the composition of the hydrocarbons in the predominantly acidlayer, this layer was mixed with ice and the resultant aqueous acidphase was extracted wih n-pentane to recover the liberated hydrocarbons.The hydrocarbons derived from the predominantly hydrocarbon layer in thereactor and from the acid phase were separately fractionated through acolumn of 30 theoretical plates to obtain an analysis by carbon number.Although 50 mol percent, each, of mesitylene and hexamethylbenzene werecharged to the reactor, 81 mol percent of hexamethylbenzene and only 19mol percent of mesitylene were found in the liquid hydrogen fluoridesolution produced in the reaction and 88 mol percent of mesitylene and12 mol percent of hexamethylbenzene were found in the predominantlyhydrocarbon layer after the reaction. This indicates thathexamethylbenzene reacts selectively with BFs and HF to form anHF-soluble complex even in the presence of a relatively basichydrocarbon such as mesitylene.

The preparative method of passing BFz into a slurry of hexamethylbenzeneand liquid HP is well adapted to a study of the nature of the resultantcomplex compound. In this method, increments of BF3 can be added to theslurry and the vapor pressure of the reaction system can be measuredafter each addition. By this method it can .readily be determined thatthe complex compound which ,is formed is exceptionally stable and thatit contains 1 mol of BF3 per mol of hexamethylbenzene. In anillustrative experiment, 20 grams of hexamethylbenzene and 228.5 gramsof liquid HF were placed in a magneticallystirred copper flask and thevapor pressure of the mixture was determined at C. Increments of BB;were added and the vapor pressure of the system was measured at 0 C.after each addition, the data obtained being presented in Table 1 below.

In the figure the total pressure is plotted against the mol ratio of BF?to hexamethylbenzene. The shape of the vapor pressure curve shows thatthe BF; is absorbed as it is added until one mol of BF3 per mol ofhexamethylbenzene is present. Then, as more BF3 is added, the BR;partial pressure increases rapidly along the straight line according toHenrys law.

Methyl-substituted benzenes, particularly those containing two or moremethyl substituents, can be selectively extracted by mixtures of liquidHF and BFs, for example as described in S. N. 46,123 of Bernard H.

Shoemaker, filed August 25, 1948, now abandoned in favor of Serial No.309,400 filed September 13, 1952. The selectivity of extraction of onemethyl-substituted benzene from another can be quantitatively describedby means of the single plate separation factor, alpha, which can bedefined as the mol ratio of two methylsubstituted benzenes in theextract (predominantly liquid HF) layer divided by their mol ratio inthe raflinate (predominantly hydrocarbon) layer. In Table 2 arepresented alpha values of the various methyl-substituted benzenesrelative to the alpha value of p-xylene, which is adopted as thestandard, since it is the first member of this homologous series toevidence appreciable basicity The relative basicity of hexamethylbenzenetowards HF-BFs mixtures is astounding upon comparison with the basicityof the other methyl-substituted benzenes and is reflected in the easewith which it forms the complex compound and the relatively highstability of the complex compound.

The properties of the hexamethylbenzeneHRBFg complex make it suitablefor many practical applications. It is especially valuable as a'catalystto be used for certain types of alkylation and polymerization reactionswhich ordinarily are catalyzed by small amounts of HF-BFa. In the formof the hexamethylbenzene complex an equimolar mixture of HF and BFs maybe transported or stored conveniently under relatively low pressure andmay be added accurately in controlled amounts to. a reaction mixture.Also, because of its relatively high stability, the hexamethylbenzenecomplex will maintain the low concentration of HF and BF: necessary insome processes for catalyzing a desired reaction and yet will avoidundesirable side-reactions induced by high catalyst concentrations.

The hexamethylbenzene complex is also useful in catalyzing reactionsrequiring an equimolar mixture of HF and BFs in high concentrations. TheHF and BF; are transported to the site of operations in the form of theeasily handled hexamethylbenzene complex and are there generated in thefree condition by heating the complex to temperatures between about 200and about 275 C. The evolved HF and BF; are passed into the reactionmixture and the hexamethylbenzene is recovered for reuse.Hexarnethylbenzene is a very stable compound and, at the temperaturesrequired for the substantial dissociation of its HF-BF3 complex, willnot crack or disproportionate even in the presence of HF and BF3.

The hexamethylbenzeneBFsHF complex compound, particularly in solution inexcess liquid HF, may be employed as a solvent for the selectiveextraction of aromatic hydrocarbons from petroleum stocks which alsocontain saturated hydrocarbons. The aromatic hydrocarbon may berecovered from the solvent by contacting the extract phase with anonaromatic counter-solvent such as petroleum ether or ligroin. Of allthe possible alkylbenzene-BFs-HF complexes, the most suitable for use asan aromatic extractant is the hexamethylbenzene.BF3.HF complex compound.Since hexamethylbenzene is the most basic of all the methylbenzenes itcannot be replaced from its complex compound with BF? and HF by anyother methylbenzene which is present in the stock charged to theextraction process. Also, since hexamethylbenzene contains no ethyl orhigher alkyl substituaveaon ent groups which we have found todisproportionate readily in the presence of liquid HF and BF:;,hexamethylbenzene will not be involved in alkyl transferring reactionsin the course of the extraction operation.

In a typical application of the aromatic extractive properties of thehexamethylbenzeneBFzHF complex compound, a charging stock comprisingprincipally aromatic and saturated hydrocarbons, which may be any lowsulfur petroleum fraction up to and including a gas oil, is passed intothe lower portion of an extraction column wherein it passes through anextract layer and is countercurrently contacted with a descending streamof hexamethylbenzene.BF3.HF dissolved in excess liquid HF which isintroduced into the upper portion of the extraction column. Preferably,the mol ratio of hexamethylbenzene to BF3 in the solvent is 1.0 and themol ratio of HF to BF is maintained between about 2 and about 16,preferably between about 4 and about 12. Extraction may be effected attemperatures between about C. and about 50 C. under pressure sutficientto maintain a substantial proportion of the solvent in the liquid phase,usually pressures between about 0 and about 50 p. s. i. g. Aninteresting and valuable feature of the complex compound-HF mixedsolvent is that the complex compound of hexamethylbenzene, BF3 and HFsubstantially lowers the vapor pressure of liquid HF, thus facilitatingextraction at relatively low pressures, compared to the pressures whichwould necessarily be employed when HF alone is employed as the solvent.The ability to operate the extraction system at relatively low pressureappreciably reduces the cost of the extraction equipment. After contactwith the descending acidic solvent stream, the dearomatized or partiallydearomatized hydrocarbons are withdrawn from the upper portion of theextraction column and sent to a raffinate stripper or to aneutralization zone to remove any small remaining amount of HP. Theextract layer is removed from the bottom of the extraction column andintroduced into the upper portion of a second extraction column whereinits is countercurrently contacted with a nonaromatic counter-solventhaving a different boiling range from that of the hydrocarbon chargingstock fed to the first extraction column. The nonaromaticcounter-solvent may be saturated, i. e., a paraffinic orcycloparaflinic, hydrocarbon or hydrocarbon mixture, e. g., liquefied,normally gaseous paraffins such as propane, n-butane, isobutane;normally liquid saturated hydrocarbons, such as n-pentane, isopentane,n-hexane, Z-methylpentane, methylcyclopentane, dimethylcyclopentanes,cyclohexane, saturated naphthas and the like. The counter-solventextraction operation may be effected at temperatures between about 10 C.and about 50 C. and pressures suificient to maintain the liquid phase. Asolution of aromatic hydrocarbons in the counter-solvent is withdrawnfrom the upper portion of the second extraction column and passed to afractionating column. Here the aromatic hydrocarbons and counter-solventare separated by fractional distillation. The counter-solvent passesoverhead together with dissolved HF and is recycled to the lower portionof the second extraction column. The aromatic hydrocarbon fraction isaftertreated to remove any residual HF by conventional techniques, forexample, neutralization with caustic, absorption in NaF, defluorinationby the use of etched aluminum surfaces, bauxite, lime, etc. TheHF-complex compound solvent is withdrawn from the lower end of thesecond extraction column and recycled to the first extraction column.

The above-described extraction process may most profitably be applied tothe separation of aromatic hydrocarbons from the gasoline boiling rangematerial produced in catalytic cracking or hydroforming. It may also beused to dearomatize heater oils and light gas oils to produce higherquality burning oils or diesel oils. It v ill be apparent that theextraction equipment may be of any variety conventionally employed orknown and that the countercurrent process and equipment described aboveare purely illustrative. Thus, it will be apparent that in a. batchextraction system the solvent could be formed in situ by mixing thecharging stock, hexamethylbenzene, HF and B1 3, eifecting contacting,and then allowing the mixture to settle in the same or a difierentvessel.

From the above description of the preparation ofhexamethylbenzeneBFsl-IF complex, it will be apparent that thepreparative methods may be employed as a means of selectively removingBFa from gas streams containing the same, for example from gas streamsderived from processes in which ER is employed as a catalyst, such asvent gases from polymerization, cracking, alkylation or other reactionsin which BFs has been employed at a catalytic medium. In order toregenerate BFz from its complex with hexamethylbenzene, the complex issubjected to pyrolysis, usually at temperatures between about 200 C. andabout 275 C. Reduced pressures and the removal of BFs as formedfacilitate the pyrolysis process. The pyrolysis may also be facilitatedby the employment of stripping gases which strip out the BFs as formedand which can be readily separated from BF by fractional liquefaction orotherwise. Thus, for example, hot HF as a vapor or gas, for example, attemperatures between about C. and about 225 C., may be passed throughthe complex in the decomposition zone and thereafter separated from theBFs which it has stripped by fractional liquefaction, following whichthe HF can be reheated and recycled to the pyrolysis zone.

This application is a continuation of application Serial No. 146,776filed by us on February 28, 1950, now abandoned.

Having thus described our invention, what we claim is:

1. As a new composition of matter, a complex compound having themolecular formula hexamethylbenzeneBFal-IF.

2. As a new composition of matter, a solution of a complex compoundhaving the molecular formula hexamethylbenzeneBFsHF in liquid hydrogenfluoride, said liquid hydrogen fluoride being in excess of the amountrequired to form said complex compound.

Clement et al.: Compte rend., volume 206, pp. 610-612 1938).

1. AS A NEW COMPOSITION OF MATTER, A COMPLEX COMPOUND HAVING THEMOLECULAR FORMULA HEXAMETHYLBENZENE.BF3HF.
 2. AS A NEW COMPOSITION OFMATTER, A SOLUTION OF A COMPLEX COMPOUND HAVING THE MOLECULAR FORMULAHEXAMETHYLBENZENE.BF3HF IN LIQUID HYDROGEN FLUORIDE, SAID LIQUIDHYDROGEN FLUORIDE BEING IN EXCESS OF THE AMOUNT REQUIRED TO FORM SAIDCOMPLEX COMPOUND.